1. Field of the Invention
The present invention relates generally to a battery charging circuit, and is directed more particularly to a battery rapid charging circuit of a constant voltage type by which a battery can be charged rapidly.
2. Description of the Prior Art
In the art, there are known two methods to charge a battery, that is, a constant current charging method and a constant voltage charging method. The constant current charging method is such a method to charge the battery with a relatively small and substantially constant current, by which even if the battery is further charged after its charging is completed, the battery is not damaged substantially by an excessive charging and hence this constant current charging method is a safe charging method. However, this constant current charging method can not be free from such a drawback that a long period of time, for example, 15 hours is required for the battery to be charged completely. On the other hand, the constant voltage charging method is such a method that the battery is charged by a substantially constant voltage by which if a voltage higher than the terminal voltage of the battery, which is completely charged, is used, the battery can be charged up in a short period of time, for example, less than one hour. This charging method, however, proposes such a problem that if the battery is charged continuously after it has been charged up, the battery generates heat due to an excessive charge and accordingly, the battery will be damaged. For this reason, this constant voltage charging method is not employed practically.